1. Field of the Invention
The present invention relates to a hybrid vehicle which is provided with both an engine and an electric motor.
2. Conventional Art
As a driving system for achieving a low fuel cost with an engine, a hybrid vehicle which utilizes a driving force of an electric motor is in use, and a variety of types therefor such as a series type and a parallel type have been proposed.
In the series type hybrid vehicle, driving of the vehicle is performed only by the electric motor and charging of a battery is performed by the engine driven generator. In the parallel type hybrid vehicle, driving of the vehicle is performed by both the engine and the electric motor or one of them. In both types, the electric motor is operated as a electric generator during deceleration and downhill running of the vehicle, and the energy recovered is regenerated to charge the battery.
However, when a downhill running continues long, the battery is almost charge to its full level and the generated energy sometimes can not be used for the charging. Therefore, in view of such cases a method is proposed in which a charging rate of the battery is in advance reduced before a possible downhill running.
JP-A-8-126116 (1996) discloses a method in which a target value of battery charging rate is set based on altitude information at a travelling route to be advanced from the current position by making use of a navigation device.
JP-A-8-223705 (1996) discloses a method in which an energy balance of a battery is in advance calculated in such a case when a travelling route of the vehicle is determined beforehand such as a bus on a regular route, and the motor torque is controlled based on a difference from the estimated predetermined value.
Further, JP-A-11-8909 (1999) discloses a method for a series type hybrid vehicle with no navigation information in which after an inclination of an uphill is estimated according to power consumption of the motor and vehicle speed and energy would be regenerated during downhill running is predicted, a generation start charging rate for the engine driven generator is set.
Among the methods referred to above, the method utilizing the navigation information can not be applied to a vehicle to which no navigation system is installed. Further, even if a navigation system is installed, the travelling route is not always set, therefore, in such cases the method can not be applied. Still further, it is rare for a common vehicle that the travelling route is known in advance as the bus on a regular route, therefore, the method of calculating beforehand the energy balance of a battery generally can not be applied.
Further, the method of estimating the inclination without using navigation information only suggests the setting method of generation start charging rate in a series type hybrid vehicle, therefore, of which method can not be applied to a parallel type hybrid vehicle. Further, it is not necessarily true that after uphill climbing downhill rolling comes, in some cases a running on a flat road follows for a relatively long period, JP-A-11-8909 (1999) fails to disclose a proper battery charging rate control in such cases.
An object of the present invention is to provide a hybrid vehicle in which regenerative energy to be recovered during downhill rolling can be utilized effectively which is applicable both for the parallel type hybrid vehicle and the series type hybrid vehicle as well as even applicable for a case where no navigation system is installed and a travelling route ahead is unclear.
Another object of the present invention is to provide a hybrid vehicle which can perform a proper control of a target charging rate even in a case where after climbing an uphill no downhill rolling follows for a comparatively long period, and which can prevent such as deterioration of fuel economy and life time reduction of the battery.
As a measure for solving the problems in a hybrid vehicle which comprises an engine which generates driving energy for driving a vehicle; a speed changer which changes revolution speed of the engine and transmits driving force to wheels; an electric motor which increases or decreases driving force of the wheels; a battery which supplies electric power for driving the electric motor as well as is used to be charged by regenerative electric power; and a battery control means which controls a charging rate of the battery, the present invention is further provided with an altitude calculating means which calculates altitude of the vehicle, wherein the battery control means sets a charging rate target value or a charging rate upper limit value based on the calculated altitude.
Further, in such instance, the charging rate target value or the charging rate upper limit value is set based on a difference between an average altitude calculated according to past altitude history and the present altitude of the vehicle.
The altitude calculating means performs the calculation based on information from GPS or information of driving torque and vehicle speed of the vehicle. As the driving torque of the vehicle a driving torque command value is used. Alternatively, the driving torque of the vehicle is estimated from a motor torque.
With these methods, even in a parallel type hybrid vehicle and in a case where no navigation system is installed and a travelling route ahead is unclear, the charging rate target value as well as the charging rate upper limit value of the battery can be varied based on the present and past altitude information, accordingly, regenerative energy recovered during downhill rolling can be effectively stored in the battery.
Further, in a case where after performing an uphill climbing no downhill rolling follows for a comparatively long period, the charge rate target value is gradually returned to the original value depending on the travelling distance, therefore, there never occurs that the charging rate remains low, thereby, the deterioration of fuel economy as well as the battery life time reduction can be prevented.